This invention relates generally to transducer systems for measuring physical variables and, more particularly, to systems of this kind that transmit a modulated light beam along an optical fiber.
Optical transducer systems of this particular kind have been used in the past in the medical field for such applications as measuring a patient's blood pressure, intra-cranial pressure, body temperature, etc. The typical system includes a catheter comprised of two sets of optical fibers located within a resilient sheath, which is adapted for insertion into a patient's body. One set of fibers transmits a light beam to a transducer located at the remote end of the catheter, and the other set of fibers returns a modulated light beam from the transducer. The transducer modulates the beam by reflecting to the second set of fibers a proportion of the light beam that varies in accordance with the variable being measured. A photosensor senses the intensity of the returned light beam, to produce a signal indicative of the variable.
Fiber-optic transducer systems such as the one described above have not proven to be entirely satisfactory, and have not as yet met with widespread acceptance. One reason for this apparent lack of acceptability is believed to be that bending of the catheter can affect the intensity of the light beam returned from the transducer. The user cannot be sure whether a particular drop in signal level is due to an actual change in the variable being measured or to bending of the catheter. In addition, movement of the catheter can modulate the intensity of the returned light beam and thereby make it difficult to measure the variable accurately.
It should therefore be appreciated that there is a definite need for a fiber-optic transducer apparatus that is not susceptible to output signal variations caused by bending or movement of the fibers. The present invention fulfills these needs.